Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Cr”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Observations of a Cast Cu-Cr-Zr Alloy

Prior work has demonstrated that Cu-Cr-Nb alloys have considerable advantages over the copper alloys currently used in regeneratively cooled rocket engine liners. Observations indicated that Zr and Nb have similar chemical properties and form very similar compounds. Glazov and Zakharov et al. reported the presence of Cr2Zr in Cu-Cr-Zr alloys with up to 3.5 wt% Cr and Zr though Zeng et al. calculated that Cr2Zr could not exist in a ternary Cu-Cr-Zr alloy. A cast Cu-6.15 wt% Cr-5.25 wt% Zr alloy was examined to determine if the microstructure developed would be similar to GRCop-84 (Cu-6.65 wt% Cr-5.85 wt% Nb). It was observed that the Cu-Cr-Zr system did not form any Cr2Zr even after a thermal exposure at 875 C for 176.5 h. Instead the alloy consisted of three phases: Cu, Cu5Zr, and Cr.

Ellis, David L.↗
NASA NTRS2008

Experimental Constraints on the Partitioning and Valence of V and Cr in Garnet and Coexisting Glass

A series of experiments with garnet and coexisting melt have been carried out across a range of oxygen fugacities (near hematite-magnetite (HM) to below the iron-wustite (IW) buffers) at 1.7 GPa to study the partitioning and valence of Cr and V in both phases. Experiments were carried out in a non end loaded piston cylinder apparatus, and the run products were analyzed with electron microprobe and xray absorption near edge structure (XANES) analysis at beamline 13-ID at the Advanced Photon Source of Argonne National Lab. The valence of vanadium and chromium were determined using the position and intensity of the Ka pre-edge peaks, calibrated on a series of Cr and Vbearing standard glasses. This technique has been applied to V and Cr in glasses and V in spinels previously, and in these isotropic phases there are no orientational effects on the XANES spectra (Righter et al., 2006, Amer. Mineral. 91, 1643-1656). We also now demonstrate this to be true for V and Cr in garnet. Also, previous work has shown that V has a higher valence in the glass (or melt) than in the coexisting spinel. This is also true for V in garnet-glass pairs in this study. Vanadium valence in garnets varies from 2.7 below the IW buffer to 3.7 near HM, and for coexisting glass it varies from 3.2 to 4.3. Vanadium valence measured in some natural garnets from mantle localities indicates V in the more reduced range at 2.5. Comparisons will be made between fO2 estimated from V valence and other methods for garnet-bearing mantle samples. In contrast, Cr valence measured in garnet and coexisting glass for all experimental and natural samples is 2.9- 3.0, suggesting that the valence of Cr does not vary within either phase across a large fO2 range. These results demonstrate that while V varies from 2+ to 3+ to 4+ in garnet-melt systems, Cr does not, and this will ultimately affect the partitioning behavior of these two elements in natural systems. Garnet/melt D(Cr) are between 12 and 17 across this range of fO2, whereas D(V) has the highest partition coefficient approx.3, near the IW buffer where the valence of V is almost entirely 3+.

Righter, K.↗
NASA NTRS2003

Analyzing Discrepancies in a Software Development Project Change Request (CR) Assessment Process and Recommendations for Process Improvements

The Change Request (CR) assessment process is essential in the display development cycle. The assessment process is performed to ensure that the changes stated in the description of the CR match the changes in the actual display requirements. If a discrepancy is found between the CR and the requirements, the CR must be returned to the originator for corrections. Data was gathered from each of the developers to determine the type of discrepancies and the amount of time spent assessing each CR. This study sought to determine the most common types of discrepancies, and the amount of time required to assessing those issues. The study found that even though removing discrepancy before an assessment would save half the time needed to assess an CR with a discrepancy, the number of CR's found to have a discrepancy was very small compared to the total number of CR's assessed during the data gathering period.

Cunningham, Kenneth James↗
NASA NTRS2011

High-Temperature Thermometer Using Cr-Doped GdAlO3 Broadband Luminescence

A new concept has been developed for a high-temperature luminescence-based optical thermometer that both shows the desired temperature sensitivity in the upper temperature range of present state-of-the-art luminescence thermometers (above 1,300 C), while maintaining substantial stronger luminescence signal intensity that will allow these optical thermometers to operate in the presence of the high thermal background radiation typical of industrial applications. This objective is attained by using a Cr-doped GdAlO3 (Cr:GdAlO3) sensor with an orthorhombic perovskite structure, resulting in broadband luminescence that remains strong at high temperature due to the favorable electron energy level spacing of Cr:GdAlO3. The Cr:GdAlO3 temperature (and pressure) sensor can be incorporated into, or applied onto, a component s surface when a non-contact surface temperature measurement is desired, or alternatively, the temperature sensor can be attached to the end of a fiber-optic probe that can then be positioned at the location where the temperature measurement is desired. In the case of the fiber-optic probe, both the pulsed excitation and the luminescence emission travel through the fiber-optic light guide. In either case, a pulsed light source provides excitation of the luminescence, and the broadband luminescence emission is collected. Real-time temperature measurements are obtain ed using a least-squares fitting algorithm that determines the luminescence decay time, which has a known temperature dependence established by calibration. Due to the broad absorption and emission bands for Cr:GdAlO3, there is considerable flexibility in the choice of excitation wavelength and emission wavelength detection bands. The strategic choice of the GdAlO3 host is based on its high crystal field, phase stability, and distorted symmetry at the Cr3+ occupation sites. The use of the broadband emission for temperature sensing at high temperatures is a key feature of the invention and is novel since broadband luminescence emission normally shows severe thermal quenching. The tightly bound AlO6 octahedra in GdAlO3 results in a larger energy barrier to nonradiative decays than in other materials and therefore makes using broadband emission for temperature sensing possible at high temperatures. This approach results in a substantial increase in temperature capability. For example, the most commonly used Cr-doped crystal used for luminescence-based temperature measurements, ruby, has only been demonstrated up to 600 C, whereas the Cr:GdAlO3 optical thermometer under development has already been shown to exhibit useful luminescence up to 1,300 C. Because GdAlO3 is non-reactive and is stable in harsh, high-temperature environments, sensors composed of Cr:GdAlO3 will be very well suited for remote high-temperature measurements in engine or industrial environments where its intense high-temperature luminescence will stand out above significant thermal radiation background levels.

Eldridge, Jeffrey↗
DOE OSTI2020

Materials Data on Cr(PS3)3 by Materials Project

Cr(PS3)3 crystallizes in the triclinic P1 space group. The structure is one-dimensional and consists of one Cr(PS3)3 ribbon oriented in the (0, 0, 1) direction. there are four inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded in a distorted see-saw-like geometry to four S2- atoms. There are two shorter (2.38 Å) and two longer (2.39 Å) Cr–S bond lengths. In the second Cr3+ site, Cr3+ is bonded to five S2- atoms to form CrS5 square pyramids that share edges with two PS4 tetrahedra. There are a spread of Cr–S bond distances ranging from 2.31–2.42 Å. In the third Cr3+ site, Cr3+ is bonded to five S2- atoms to form distorted CrS5 trigonal bipyramids that share an edgeedge with one PS4 tetrahedra. There are a spread of Cr–S bond distances ranging from 2.33–2.41 Å. In the fourth Cr3+ site, Cr3+ is bonded to one P5+ and four S2- atoms to form distorted CrPS4 trigonal bipyramids that share edges with two PS4 tetrahedra. The Cr–P bond length is 2.24 Å. There are a spread of Cr–S bond distances ranging from 2.38–2.41 Å. There are twelve inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four S2- atoms to form edge-sharing PS4 tetrahedra. There are a spread of P–S bond distances ranging from 2.00–2.13 Å. In the second P5+ site, P5+ is bonded to four S2- atoms to form edge-sharing PS4 tetrahedra. There are a spread of P–S bond distances ranging from 2.01–2.12 Å. In the third P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share an edgeedge with one CrS5 square pyramid. There are a spread of P–S bond distances ranging from 2.02–2.09 Å. In the fourth P5+ site, P5+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are a spread of P–S bond distances ranging from 2.04–2.25 Å. In the fifth P5+ site, P5+ is bonded in a distorted water-like geometry to two S2- atoms. There are one shorter (2.08 Å) and one longer (2.10 Å) P–S bond lengths. In the sixth P5+ site, P5+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are a spread of P–S bond distances ranging from 2.00–2.17 Å. In the seventh P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share an edgeedge with one CrS5 trigonal bipyramid. There are a spread of P–S bond distances ranging from 1.99–2.13 Å. In the eighth P5+ site, P5+ is bonded in a distorted L-shaped geometry to one Cr3+ and two S2- atoms. There are one shorter (2.11 Å) and one longer (2.12 Å) P–S bond lengths. In the ninth P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share an edgeedge with one CrS5 square pyramid. There are a spread of P–S bond distances ranging from 2.00–2.09 Å. In the tenth P5+ site, P5+ is bonded in a distorted trigonal non-coplanar geometry to three S2- atoms. There are a spread of P–S bond distances ranging from 1.96–2.25 Å. In the eleventh P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share an edgeedge with one PS4 tetrahedra and an edgeedge with one CrPS4 trigonal bipyramid. There are a spread of P–S bond distances ranging from 2.00–2.13 Å. In the twelfth P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share an edgeedge with one PS4 tetrahedra and an edgeedge with one CrPS4 trigonal bipyramid. There are a spread of P–S bond distances ranging from 2.00–2.13 Å. There are thirty-six inequivalent S2- sites. In the first S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the second S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the third S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the fourth S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the fifth S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the sixth S2- site, S2- is bonded in a distorted water-like geometry to two S2- atoms. There is one shorter (1.94 Å) and one longer (2.04 Å) S–S bond length. In the seventh S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the eighth S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the ninth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the tenth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the eleventh S2- site, S2- is bonded in a 2-coordinate geometry to one P5+ and one S2- atom. The S–S bond length is 2.05 Å. In the twelfth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the thirteenth S2- site, S2- is bonded in a 1-coordinate geometry to one P5+ and one S2- atom. In the fourteenth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the fifteenth S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the sixteenth S2- site, S2- is bonded in a 2-coordinate geometry to one Cr3+ and one P5+ atom. In the seventeenth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the eighteenth S2- site, S2- is bonded in a water-like geometry to two P5+ atoms. In the nineteenth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the twentieth S2- site, S2- is bonded in a distorted water-like geometry to two S2- atoms. There is one shorter (1.94 Å) and one longer (2.03 Å) S–S bond length. In the twenty-first S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the twenty-second S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the twenty-third S2- site, S2- is bonded in a distorted single-bond geometry to one P5+ atom. In the twenty-fourth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the twenty-fifth S2- site, S2- is bonded in a single-bond geometry to one S2- atom. In the twenty-sixth S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the twenty-seventh S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the twenty-eighth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the twenty-ninth S2- site, S2- is bonded in a distorted single-bond geometry to one Cr3+ and one S2- atom. In the thirtieth S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the thirty-first S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the thirty-second S2- site, S2- is bonded in an L-shaped geometry to two P5+ atoms. In the thirty-third S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom. In the thirty-fourth S2- site, S2- is bonded in a 1-coordinate geometry to one Cr3+ and one S2- atom. In the thirty-fifth S2- site, S2- is bonded in a single-bond geometry to one S2- atom. In the thirty-sixth S2- site, S2- is bonded in an L-shaped geometry to one Cr3+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry

The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. In this paper, we applied the short-lived 53 Mn- 53 Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53 Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53 Cr/ 52 Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53 Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53 Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than time estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.

58 GEOSCIENCES↗
DOE OSTI2023

Effect of chromium on corrosion resistance of Ni-Cr-Mo-Gd alloys in seawater

Neutron absorbing materials are being considered within commercial spent nuclear fuel disposal canisters to maintain nuclear subcriticality in storage. To select candidate alloys for the canisters, both neutron absorption and corrosion resistance should be considered. This work examines corrosion resistance of Ni-Cr-Mo-Gd alloys developed specifically for neutron absorption. The addition of Gd results in a secondary gadolinide phase (Ni 5 Gd) that significantly changes the corrosion properties. Testing was performed primarily in seawater at 30°C. Seawater was selected as the most prevalent terrestrial brine and is characterized by a high chloride concentration. Various electrochemical corrosion techniques were carried out to evaluate Ni-Cr-Mo-Gd alloys with different Cr compositions and investigate the role of Ni 5 Gd phase on corrosion behavior. C22 was included as a benchmark material, due to the similarity in composition and the significant corrosion data available. Here, test results showed a tendency to passivate over time which is attributed to dissolution of surface exposed Ni 5 Gd phase. Cross-sectional analysis indicated that dissolution could penetrate hundreds of micrometers deep under aggressive conditions. It was found that higher Cr variant (21.01%) showed much shallower impact, suggesting Cr prevented primary phase corrosion and thus reduced Ni 5 Gd phase dissolution. Acid pickling of the specimens showed much less dissolution for a higher Cr material and suggested some primary phase dissolution for the low Cr specimen. Acid pickled specimens showed positive shifts in the repassivation potential, suggesting increased surface passivation.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Angle-Resolved Polarized Raman Study of Layered Cr 2 Se 3

The polarization-resolved Raman spectra of two-dimensional Cr 2 Se 3 synthesized via chemical vapor deposition (CVD) and chemical vapor transport (CVT) techniques were investigated in detail. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). A distinct polarization dependence was observed in the Raman intensity of all the Cr-Cr, Cr-Se, and Se-Se modes in both samples. The observed angle-dependent Raman intensities of each peak could be related to the crystal structure-specific Raman tensor. XRD results of the bulk Cr 2 Se 3 sample synthesized via CVT confirm its trigonal crystal structure, and the Raman peaks can be fitted using the Raman tensors for the A g and E g modes for both the parallel and crossed polarizations. However, for the Cr 2 Se 3 samples directly grown on Si/SiO 2 substrates by CVD, it was necessary to assume the triclinic crystal structure in order to explain the polarized Raman dependence of all the peaks in both parallel and crossed polarization directions. Furthermore, this is the first experimental result suggesting the existence of triclinic Cr 2 Se 3 crystal structure, which has been theoretically predicted in the Materials Project database.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Temperature-dependent cavity swelling in dual-ion irradiated Fe and Fe-Cr ferritic alloys

Fe-Cr ferritic-martensitic (FM) steels are promising structural material candidates for fusion and advanced fission reactors due to their attractive mechanical properties and volumetric swelling resistance. However, significant discrepancies exist regarding the effect of solutes and irradiation temperature on cavity swelling under ion versus neutron irradiation conditions. In this study, simultaneous dual ion irradiations (8 MeV Ni 3+ ions and energy-degraded 3.5 MeV He 2+ ions) were used to quantify the cavity swelling behavior in ultra-high purity Fe and Fe-Cr alloys (3-14 wt.% Cr), Fe-10 wt.% Cr-780 wt.ppm C, and Eurofer97 FM steel. The irradiations were conducted over a wide temperature range (400-550°C) with a mid-range dose of ~30 displacements per atom (dpa) and 0.1 appm/dpa He implantation rate. Here, using state-of-the-art transmission electron microscopy (TEM), we reveal that pure Fe has a ~50°C lower peak swelling temperature difference than Fe-Cr alloys, which is attributed to higher vacancy mobility in pure Fe. Chromium solute appears to strongly suppress cavity swelling in Fe-Cr alloys for temperatures below ~470°C, but seems to have little effect or slightly enhances swelling above ~470°C. Cavities were observed in all the irradiated samples between 400-550°C. This indicates that the narrow temperature range of observable cavities reported in prior ion irradiated Fe-Cr ferritic alloy studies is likely an artifact associated with the use of low ion energies (<5 MeV), which leads to pronounced near-surface and implanted ion effects that suppress cavity swelling even at midrange depths (particularly at high temperatures).

36 MATERIALS SCIENCE↗
DOE OSTI2023

Proof-of-concept studies of novel protocols for producing highly pure 48 V from a 48 Cr/ 48 V generator

Here, the quest to improve the quality of nuclear data, such as half-lives, transition yields, and reaction cross-sections, is a shared endeavor among various areas of nuclear science. 48 V is a vanadium isotope for which experimental data on neutron reaction cross-sections is needed. However, traditional isotope production techniques cannot produce 48 V with high enough isotopic purity for some of these measurements. “Isotope harvesting” at the Facility for Rare Isotope Beams (FRIB) is a new isotope production technique that could potentially yield 48 V with the necessary purity for such studies. In this case, 48Cr would be collected and allowed to generate 48 V that can be separated from undecayed 48 Cr to yield highly pure 48 V. Thus, any protocol for producing pure 48 V via isotope harvesting would involve utilizing a separation technique that can effectively separate 48 Cr and 48 V. In this study, the radiotracers 51 Cr and 48 V were used to develop possible radiochemical separation methodologies, which can be translated to obtain high purity 48 V via this novel isotope production method. The developed protocols utilize either ion exchange or extraction chromatographic resins. Separations of 51 Cr and 48 V with AG 1-X8 anion exchange resin respectively resulted in recoveries of 95.6(26)% and 96.2(12)% with radionuclidic purities of 92(2)% and 99(1)%. An even more effective Cr and V separation was obtained with an extraction chromatographic resin (TRU resin) and 10 M HNO 3 loading solution. Here, 51 Cr and 48 V respectively had recoveries of 94.1(28)% and 96.2(13)% with high radionuclidic purities (100(2)% and 100(1)%) in small volumes (8.81(8) mL and 5.39(16) mL). This study suggests that, to maximize the yield and isotopic purity of 48 V, the best production protocol would involve utilizing two separations with TRU resin and 10 M HNO 3 to isolate 48 Cr and purify the generated 48 V.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

An In Situ , multi-electrode electrochemical method to assess the open circuit potential corrosion of Cr in unpurified molten FLiNaK

An in situ electrochemical method to investigate the time-dependent spontaneous corrosion of pure Cr in an unpurified LiF-NaF-KF eutectic salt at 600 °C was developed. A multi-electrode electrochemical cell and a dual-electrode method were utilized to detect Cr(II) and Cr(III) ions on a platinum working electrode using cyclic voltammetry as a function of exposure time and compensating for the distance from the Cr electrode. XRD was performed to characterize the crystalline composition of the exposed FLiNaK and the salt films formed on the working electrodes. The fate of all electro-oxidized Cr must be accounted for to quantify corrosion rates. The concentrations of Cr(II) and Cr(III) species obtained were compared with the gravimetric mass change and ICP-OES analysis of the residual salt. Finally, outcomes, difficulties, and limitations are discussed.

ICP-OES↗
DOE OSTI2021

An evaluation of tri-valent oxide (Cr 2 O 3 ) as a grain enlarging dopant for UO 2 nuclear fuels fabricated under reducing environment

A study was performed to evaluate the microstructure and crystallography of nominally 500–2000 Cr 2 O 3 -doped UO 2 fabricated in a temperature range of 1150–1750°C under reducing experimental conditions. We observed an increase in grain size of the samples with the increase in heat treating temperature as expected. For a given sintering temperature (1700–1750°C), an increase in the grain size was also observed with the increase in Cr 2 O 3 concentration up to a value of ~1000–1200 wppm. A decrease in fission gas release as a function of grain size was estimated for the Cr 2 O 3 -doped UO 2 samples assuming specified post-irradiation annealing conditions. A nearly linear decrease was obtained in the lattice parameter of the Cr 2 O 3 -doped UO 2 fcc phase with the increase in Cr 2 O 3 concentration, especially up to a nominal value of 1000 wppm. The lattice parameter decrease was also persistent with the increase in the average grain size as a result of addition of Cr 2 O 3 into the UO 2 lattice. An increase in the crystallite size and a decrease in the microstrain of the $fcc$ phase were observed with the increase in the average grain size of the samples, indicating a higher crystallinity of the Cr 2 O 3 -doped samples than that of the undoped UO 2 sample.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Ferromagnetic Cr 4 PtGa 17 : A Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice

Here, we describe the crystal structure and elementary magnetic properties of a previously unreported ternary intermetallic compound, Cr 4 PtGa 17 , which crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group R3m. The crystal structure is closely related to those of XYZ half-Heusler compounds, where X, Y, and Z are reported to be single elements only, occupying three different face-centered-cubic sublattices. The new material, Cr 4 PtGa 17 , can be most straightforwardly illustrated by writing the formula as (PtGa 2 )(Cr 4 Ga 14 )Ga (X = PtGa 2 , Y = Cr 4 Ga 14 , Z = Ga); that is, the X and Y sites are occupied by clusters instead of single elements. The magnetic Cr occupies a breathing pyrochlore lattice. Ferromagnetic ordering is found below T C ~ 61 K, by both neutron diffraction and magnetometer studies, with a small, saturated moment of ~0.25 μ B /Cr observed at 2 K, making Cr 4 PtGa 17 the first ferromagnetically ordered material with a breathing pyrochlore lattice. A magnetoresistance of ~140% was observed at 2 K. DFT calculations suggest that the material has a nearly half-metallic electronic structure. The new material, Cr 4 PtGa 17 , the first realization of both a half-Heusler-type structure and a breathing pyrochlore lattice, might pave a new way to achieve novel types of half-Heusler compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ligand control of low-frequency electron paramagnetic resonance linewidth in Cr(iii) complexes

Understanding how the ligand shell controls low-frequency electron paramagnetic resonance (EPR) spectroscopic properties of metal ions is essential if they are to be used in EPR-based bioimaging schemes. In this work, we probe how specific variations in the ligand structure impact L-band (ca. 1.3 GHz) EPR spectroscopic linewidths in the trichloride salts of five Cr(III) complexes: [Cr(RR-dphen) 3 ] 3+ (RR-dphen = (1R,2R)-(+)-diphenylethylenediamine, 1), [Cr(en) 3 ] 3+ (en = ethylenediamine, 2), [Cr(me-en) 3 ] 3+ (me-en = 1,2-diaminopropane, 3), [Cr(tn) 3 ] 3+ (tn = 1,3-diaminopropane, 4) [Cr(trans-chxn) 3 ] 3+ (trans-chxn = trans-(±)-1,2-diaminocyclohexane, 5). Spectral broadening varies in a nonintuitive manner across the series, showing the sharpest peaks for 1 and broadest for 5. Molecular dynamics simulations provide evidence that the broadening is correlated to rigidity in the inner coordination sphere and reflected in ligand-dependent distribution of Cr–N bond distances that can be found in frozen solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Exploring Cr and molten salt interfacial interactions for molten salt applications

Molten salts play an important role in various energy-related applications such as high-temperature heat transfer fluids and reaction media. However, the extreme molten salt environment causes the degradation of materials, raising safety and sustainability challenges. A fundamental understanding of material–molten salt interfacial evolution is needed. This work studies the transformation of metallic Cr in molten 50/50 mol% KCl–MgCl 2 via multi-modal in situ synchrotron X-ray nano-tomography, diffraction and spectroscopy combined with density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Notably, in addition to the dissolution of Cr in the molten salt to form porous structures, a δ-A15 Cr phase was found to gradually form as a result of the metal–salt interaction. This phase change of Cr is associated with a change in the coordination environment of Cr at the interface. DFT and AIMD simulations provide a basis for understanding the enhanced stability of δ-A15 Cr vs. bcc Cr, by revealing their competitive phase thermodynamics at elevated temperatures and probing the interfacial behavior of the molten salt at relevant facets. This study provides critical insights into the morphological and chemical evolution of metal–molten salt interfaces. Finally, the combination of multimodal synchrotron analysis and atomic simulation also offers an opportunity to explore a broader range of systems critical to energy applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Resilience of the Aurivillius structure upon La and Cr doping in a Bi 5 Ti 3 FeO 15 multiferroic

Here, combining the experimental techniques of high-resolution X-ray diffraction, magnetometry, specific heat measurement, and X-ray photoelectron, Raman and dielectric spectroscopy techniques, we have studied the influence of La and Cr doping on the crystal structure and magnetism of the room temperature Aurivillius multiferroic Bi 5 Ti 3 FeO 15 by investigating the physical properties of (Bi 4 La)Ti 3 FeO 15 and Bi 5 Ti 3 (Fe 0.5 Cr 0.5 )O 15 . The parent (Bi 5 Ti 3 FeO 15 ) and the doped ((Bi 4 La)Ti 3 FeO 15 and Bi 5 Ti 3 (Fe 0.5 Cr 0.5 )O 15 ) compounds crystallize in the A2 1 am space group, which is confirmed through our analysis of high-resolution synchrotron X-ray diffraction data obtained on phase-pure polycrystalline powders. We determined the oxidation states of the metal atoms in the studied compounds as Fe 3+ , Ti 4+ , Cr 3+ , and La 3+ through the analysis of X-ray photoelectron spectroscopy data. The magnetic susceptibilities of the three compounds are marked by the absence of a long-range ordered ground state, but dominated by superparamagnetic clusters with dominant antiferromagnetic interactions. This signature of short-range magnetism is also seen in specific heat as a low temperature enhancement which is suppressed upon the application of external magnetic fields up to 8 T. Our dielectric spectroscopy experiments showed that the three studied compounds display similar features in the dielectric constant measured as a function of frequency. However, upon doping La at the Bi site, the width of the ferroelectric hysteresis loop increases for (Bi 4 La)Ti 3 FeO 15 compared to that of the parent compound Bi 5 Ti 3 FeO 15 , and with Cr doping, Bi 5 Ti 3 (Fe 0.5 Cr 0.5 )O 15 becomes a leaky dielectric. The resilience of the Aurivillius crystal structure towards doping of La at the Bi site and Cr at the Fe site is clearly seen in the bulk properties of magnetic susceptibility, specific heat and the average crystal structure. The relevance of changes in the local structure is evident from our Raman spectroscopy and X-ray pair distribution function studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Cobalt ferrite nanoparticle intercalated carbon nanotubes for a nanomagnetic ultrasensitive sensor of Cr-VI in water

Nanocomposites of cobalt ferrite (CFO) magnetic nanoparticles intercalated on carbon nanotubes (CNTs) are evaluated as a nanomagnetic ultrasensitive sensor for the environmental toxin, hexavalent chromium (Cr-VI). Specifically, the structural and magnetic changes that accompany the infiltration of the CFO/CNTs by Cr-VI are presented. Extended x-ray absorption fine structure (EXAFS) shows that the atomic spacing within the CFO structure changes in the presence of Cr, suggesting that the Cr is incorporated into the nanoparticles. Vibrating sample magnetometry (VSM) reveals that CFO/CNTs composite infiltrated with Cr-VI have a 71% enhancement in saturation magnetization compared with the uninfiltrated CFO/CNTs, while small-angle neutron scattering (SANS) suggests that this magnetic enhancement is not associated with the nanoparticle lengthscales, but may arise from longer-ranged clusters. Both VSM and SANS clearly demonstrate that the Cr-doped CFO/CNTs are hysteretic with a net magnetization at remanence that is about 1/3 that of saturation, while this hysteresis is absent in the undoped CFO/CNTs. These magnetic differences at either remanence or saturation are promising for the magnetic detection of Cr-VI using CFO/CNTs sensors.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Absence of long-range magnetic order in lithium-containing honeycombs in the Li–Cr–Sb(Te)–O phases

Li 3 ((LiCr)(Te/Sb))O 6 compounds where Cr atoms along with Li and Te or Sb are part of a honeycomb and are studied using magnetic susceptibility, specific heat, x-ray photoelectron spectroscopy and neutron diffraction. The oxides stoichiometries as determined from the neutron diffraction studies are Li 4.47 Cr 0.53 TeO 6 and Li 3.88 Cr 1.12 SbO 6 with a stable oxidation state of +3 for Cr. Both the compounds crystallize in space group C2/m with intermixing of cations at the 4g sites leaving the 2a sites preferentially for Te or Sb. Again, the Li + ions alone predominantly occur in the interlayer sites. Both the compounds show a broad anomaly in specific heat at 8 K, which is robust against 8 T. A corresponding anomaly is absent in the magnetic susceptibility but recovers from its derivative, dχ(T)/dT. Here, we ascertain the magnetic anomaly temperatures (T a ) of Li 4.47 Cr 0.53 TeO 6 and Li 3.88 Cr 1.12 SbO 6 as 5.9 K and 6.7 K respectively from specific heat. Although the physical properties indicated a low temperature anomaly, neutron diffraction data did not reveal a magnetic signal or a structural anomaly down to 1.5 K. This rules out a conventional long-range ordered magnetic ground state in either compounds. Combining the results from specific heat, neutron diffraction and electron paramagnetic resonance, we put forth a scenario of depleted honeycomb lattice of Cr 3+ with predominant short-range magnetic correlations as the magnetic ground states of the title compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗